It has generally been accepted that the electroerosion technique, when applied to the machining of a 3D cavity in a workpiece, commonly requires a tool electrode three-dimensionally shaped to conform to the desired cavity in the workpiece. Thus, a conventional sinking-type or 3D EDM electrode may be a precision-machined conductive block or a sheet metal precision-deformed or plated precision-electroforming mold. Furthermore, a multiplicity of such electrodes of identical or similar configuration must be prepared in order to compensate for the wear which the electrodes suffer during the erosion process or in the interest of minimizing the machining time to achieve the end of a desired machined precision and surface finish. Preparation of such precision-formed and multiple electrodes is generally time-consuming and laborious and entails considerable skill and labor and, as a consequence, may make a desired EDM job unduly costly or often even impractical. Furthermore, the conventional sinking-type operation makes it difficult to keep the machining gap free from the debris of machined chips and other products which tend to cause machining instability.